The invention relates to an optical signalling or display device with a rasterized luminous field of a spatially defined light intensity distribution, which device with a housing comprises a matrix arranged on a printed circuit board of light sources, in particular LEDs, which can be controlled individually, in groups or as a whole, and a diffusion lens which is flat on the outside and extends over the entire luminous field, on the inside of which are formed parallel grooves with at least partly asymmetrically curved surface. A lens system comprises at least one lens. The invention further relates to a process for monitoring the light intensity of an optical signalling or display device of the generic type.
In particular, in the case of traffic signals, known rasterized luminous fields comprise high-intensity luminous points whichxe2x80x94determined by the raster in relation to resolutionxe2x80x94signal all prohibitions, dangers and information at high intensity in a stationary or moving fashion. This is done in the form of images and/or texts. The punctiform light sources are, in particular:
In a light emitting diode or LED, charge carriers in a pn junction operated in the conducting direction can assume high energy values which they re-emit in the form of light quanta. The generated light is virtually monochromatic and depends on the semiconductor material and the doping thereof. LED""s, made for example from GaP, GaAs or GaAsP, emit discrete wavelengths in the red, green, and yellow spectral range (660 to 550 nm).
The light of a single lamp can be passed to the luminous field by glass fibre technology. In the case of red-yellow-green signalling, three glass fibres are required per raster point. In general, to generate a rasterized luminous field, LED technology is preferred: it is less delicate, has a longer service life with regard to the light source, and requires less energy and maintenance than glass fibre technology.
DE, A1 2702823 disclosed for the first time an electrically illuminated signalling device which has an luminous field with a multiplicity of LEDs and a translucent or transparent cover. Each LED is assigned a spherically constructed cap of a lens extending over the entire luminous field. This solution gives high-intensity traffic signals which permit housings of substantially less depth. However, visors are still required if no or reduced visibility is desired or necessary in certain directions.
The aim of EP, A2 0694894 is a light intensity distribution adapted to the conditions without the need for complex and expensive lens systems. This is achieved by holding at least some of the LEDs inside the signalling lamp such that they can be tilted from a first to at least a second emission direction and positioned by an adjustment device. The desired emission direction is reached by means of rectilinear or rotating mechanical displacement elements. Thus it is possible to achieve a light intensity distribution largely corresponding to the requirements of the traffic participants. However, mechanically moving parts are required, a fact which is usually expensive or even disadvantageous in the medium and long term.
WO, A 96/24802 discloses prismatic toroidal lenses and a traffic signal with a luminous field composed of LEDs. Each LED contains a lens with a parabolic light-refracting surface and an outer light-refracting surface. The outer surface has an annular outer region and a central region. A specific spatially defined light intensity distribution is achieved with this special design of the lenses assigned individually to each LED. The aim of a spatially defined light intensity distribution is achieved in a relatively complicated manner with this honeycomb-shaped arrangement of a matrix of numerous, relatively complex lenses.
WO, A 97/26483 shows a lamp arrangement comprising a lens which can deflect the light in a desirable direction in order to comply with certain traffic regulations. This lens works in combination with special LEDs so that light emitted by it can be deflected. The structure of parallel grooves arranged at regular intervals in the inner area of the diffusion lens is striking. The area between the grooves is divided into two part areas. A first part area is designed flat or curved, a second part area has fluting running in the transverse direction of the grooves.
The inventors have set themselves the task of creating a device of the type stated initially and a process which meets the requirements of all observers in relation to the spatial light intensity distribution in a simple, optimum way without the need for delicate mechanisms or complex arrangements of special individual lenses. Furthermore, it should fulfil the latent need for continuous monitoring of the light intensity in particular of an ageing optical signalling or display device in order to be able to intervene immediately a critical threshold is passed.
With reference to the device, the task is solved according to the invention in that the circuit board is formed at least partly transparent and the flat area between the grooves of the diffusion lens runs parallel or at a slight angle to the outer flat surface. Special forms and developments of the device are the subject of the dependent claims.
A luminous field of a traffic signal is for example round and preferably has SMT or chip-on-board LEDs. The diameter of a luminous field is suitably approximately 200 mm but for larger signals can also be approximately 300 mm and have a correspondingly larger number of LEDs. Triangular and square luminous fields for example are dimensioned correspondingly.
The LEDs are arranged in the known manner on a printed circuit board. Each LED can emit white light or light of a particular colour. Also an LED of multipartite construction can also emit more than one colour, for example red and yellow, red and green or yellow and green. Tripartite LEDs can emit all three colours, for example red, yellow and green, which are required for traffic control signals.
In almost all optical signalling or display devices, it is desirable for the light intensity distribution to be optimised in energy terms and suitable for users. In particular with traffic signals, light beams emitted upwards and sharply to the side have practically no use or even a disruptive effect. The light beams are focused horizontally or downwards, whereby a substantially higher light intensity is achieved for the same energy consumption. An optimum light intensity distribution in percentage for luminous field diameters of 200 and 300 mm is standardized in DIN 67527 part 1. Above a vertical angle of +3xc2x0 and below xe2x88x9210xc2x0, the light intensity is very low, as is the case for lateral angles greater than xc2x120xc2x0. Without screening visors, the car driver sees a traffic signal at an optimum distance with increased light intensity, but on a side road or from a dwelling situated next to the road, the signal on the main road is scarcely noticed.
All lenses, because of the good machinability, consist in particular of a transparent plastic or plexiglas. Lenses made from conventional glass or ceramic can certainly fulfil the purpose of the invention, but they are substantially more difficult to machine, and therefore more expensive.
Particularly in the case of the LEDs which emit white light, the lenses can be homogeneous or coloured in sectors and thus filter out a portion of the white light, whereby the original white light appears coloured. In the case of LEDs which emit coloured light and/or a plurality of lenses, it is also possible to form entire colour combinations.
The diffusion lens is mounted with the smooth side facing outwards, i.e. pointing away from the LEDs. This facilitates cleaning work in the event of dust or dirt. Moreover, the diffusion lens can also function thus as a cover plate but this should not prevent the additional use of such a cover plate if required. The internal parallel grooves extend over the entire diffusion lens, and at least up to an annular edge region. The grooves are constructed at least partially with a curved cross-section but also with a flat part area such that the light beams emitted by the LEDs are deflected in a light intensity distribution which largely corresponds to DIN 67527 part 1. The optimum geometry of the groove cross-section and the flat area connecting the grooves is established empirically by trial and calculation. One feature essential to the invention is the asymmetry, part of the light emitted by the LEDs is deflected and added to the non-deflected light. In this way a gain factor of up to 2 can be achieved. In this case, the diffusion lens is also termed a doubler lens.
According to an advantageous embodiment of the invention, it is possible to arrange an intermediate lens which collects the light emitted by the LEDs and feeds it to the outer diffusion lens. A broad emission characteristic can thus be achieved. When several lenses are used, the latter are preferably integrated on a common carrier.
As is already evident from the preceding statements, the main use of the optical signalling or display device is in rail or road traffic as a traffic signal or traffic light, to perform all signalling legally prescribed or decreed of:
orders such as red-yellow-green traffic routing, speed restrictions and overtaking bans,
risks such as height restrictions under bridges and the risk of skidding, and
information conveyed by stationary or moving images and/or alphanumeric texts such as displaying lane changes by moving arrows, advance warning of roadworks, tunnels, icing or wind gusts, by remote control to be clearly visible and relevant.
In addition to new fitments, the optical signalling and display devices according to the invention can also be used for conversion, where the low power consumption of 8 to 12 W can be achieved by interposing an ohmic consumer. With this low power consumption for example, a light intensity of approximately 500 cd can be achieved by using a light distribution in accordance with DIN 67527 part 1. The usual service life for LEDs of more than 10 years can be achieved with no further measures.
The device according to the invention can however be used not only in traffic but also on and in buildings, in particular public buildings, on lifts and escalators, on ski lifts etc. as a display device.
With reference to the process for monitoring the light intensity of an optical signalling or display device with a rasterized luminous field, the task according to the invention is solved in that sensors arranged on the rear of a printed circuit board detect light beams emitted rearwards by light sources arranged on the at least partially transparent circuit board, and/or light beams which are reflected at the light-collecting intermediate lens or, if this is not used, at the diffusion lens and pass through the circuit board, and convert these into signals which are passed to an electronic system which, when a defined threshold is passed, initiates action in the form of increased electrical power, advance warning and/or disconnection.
Various causes can reduce the light intensity of an optical signalling or display device, for example age or coating of the transparent outer lens or cover glass with dust and/or dirt. In order to guarantee the user a constantly unambiguous operating state, the light intensity is monitored optically according to the invention where the light intensity emitted by LEDs is detected in the housing, also termed the sealing cover, of the optical signalling and display device by sensors arranged therein, and converted into preferably electric signals. A microprocessor compares the signals with prescribed nominal values.
Measures are instituted for example by the electronic system, for example a microprocessor, arranged inside or outside the optical signalling and display device when the value falls by a threshold value of for example at least around 30%, in particular in the range from 40 to 60% of the nominal value. The electric power is reduced accordingly for example when it is no longer required at this level after cleaning of the signal. An advance warning can be given optically and/or acoustically in a control centre. If the fault is not rectified within a relatively short time, the system is shut down or, in the case of traffic lights, switched to a yellow flashing light. Simpler signalling systems can be shut down without advance warning or increase in electrical power when the threshold value is no longer reached.
The process according to the invention for monitoring the light intensity can be applied in all optical signalling or display devices having a rasterized luminous field by applying expert knowledge.